/*
 * Copyright (C) 2011 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.inject.spi;

import com.google.inject.Binding;
import com.google.inject.Provider;
import com.google.inject.Scope;

import java.util.List;

/**
 * Listens for provisioning of objects. Useful for gathering timing information
 * about provisioning, post-provision initialization, and more.
 * 
 * @author sameb@google.com (Sam Berlin)
 * @since 4.0
 */
public interface ProvisionListener {

    /**
     * Invoked by Guice when an object requires provisioning. Provisioning occurs
     * when Guice locates and injects the dependencies for a binding. For types
     * bound to a Provider, provisioning encapsulates the {@link Provider#get}
     * method. For toInstance or constant bindings, provisioning encapsulates
     * the injecting of {@literal @}{@code Inject}ed fields or methods.
     * For other types, provisioning encapsulates the construction of the
     * object. If a type is bound within a {@link Scope}, provisioning depends on
     * the scope. Types bound in Singleton scope will only be provisioned once.
     * Types bound in no scope will be provisioned every time they are injected.
     * Other scopes define their own behavior for provisioning.
     * <p>
     * To perform the provision, call {@link ProvisionInvocation#provision()}.
     * If you do not explicitly call provision, it will be automatically done after
     * this method returns.  It is an error to call provision more than once.
     */
    <T> void onProvision(ProvisionInvocation<T> provision);

    /**
     * Encapsulates a single act of provisioning.
     *
     * @since 4.0
     */
    public abstract static class ProvisionInvocation<T> {

        /**
         * Returns the Binding this is provisioning.
         * <p>
         * You must not call {@link Provider#get()} on the provider returned by
         * {@link Binding#getProvider}, otherwise you will get confusing error messages.
         */
        public abstract Binding<T> getBinding();

        /** Performs the provision, returning the object provisioned. */
        public abstract T provision();

        /** Returns the dependency chain that led to this object being provisioned. */
        public abstract List<DependencyAndSource> getDependencyChain();

    }
}
